Composite structural member for a building structure

A method for use in designing a composite rafter for a building structure, wherein the composite rafter is required to have a first member with a first end region and a second end region, a second member with a first end region and a second end region, the first end region of the first member connected or connectable to a support portion of the building, the second end region of the first member connected or connectable to the first end region of the second member, and the design of the rafter is required to be such that, in use, the second end region of the second member is located higher than the first end region of the first member, the method comprising:

• assessing bending moments which the rafter is required to be capable of resisting at various points or regions along the length of the rafter;
• determining at least one point or region along the length of the rafter which is to be provided where the bending moment which the rafter is required to resist is maximum;
• identifying a first type of structural component with a first bending moment bearing capacity which is capable of resisting said maximum bending moment, and selecting a structural component of the first type to use as the first member of the rafter;
• determining at least one point or region along the length of the rafter which is to be provided where the bending moment which the rafter is required to resist is substantially smaller than said maximum bending moment;
• identifying a second type of structural component which is different from the first type of structural component and wherein the second type of structural component has a second bending moment bearing capacity which is capable of resisting said smaller bending moment but not necessarily capable of resisting said maximum bending moment, and selecting a structural component of the second type to use as the second member of the rafter;
• and
• determining a position, along the length of the rafter which is to be provided, at which to provide a join or transition between the first member and the second member, wherein the position of the join or transition is such that bending moments in portions of the rafter formed by the second member do not exceed the second bending moment bearing capacity.